1. Field of the Invention
The invention concerns a magnetic resonance apparatus, a local coil positioning device and a local coil for use in/with the magnetic resonance apparatus.
2. Description of the Prior Art
Magnetic resonance (MR) is a known modality with which images of the inside of an examination subject can be generated. Described simply, the examination subject is positioned in a strong, static, homogeneous basic magnetic field (field strengths from 0.2 Tesla to 7 Tesla and more) in an MR apparatus (scanner) so that his nuclear spins in the subject align along the basic magnetic field. Radio-frequency excitation pulses are radiated into the examination subject to trigger nuclear magnetic resonances. The triggered nuclear magnetic resonances are measured (detected) and MR images are reconstructed based thereon. For spatial coding of the measurement data, rapidly switched magnetic gradient fields are superimposed on the basic magnetic field. The acquired measurement data are digitized and stored as complex numerical values in a k-space matrix. By means of a multidimensional Fourier transformation, an associated MR image can be reconstructed from the k-space matrix populated with such values.
For an improved, spatially precise excitation and measurement of the nuclear magnetic resonances, local coils are used that are positioned directly on the patient to be examined, around an area to be examined (for example knee, head, abdomen etc.). Furthermore, it is sought to optimally position the area (volume) of the patient to be examined (and therefore, if applicable, the local coil) in the center of the examination region of the magnetic resonance apparatus, since the best measurement conditions prevail in that examination region.
For this purpose, it is known to focus on the area of the patient to be examined by means of a light-beam localizer that is located outside of the examination region of the magnetic resonance apparatus at a defined distance from its center, in order to thus determine a travel path that will bring the area to be examined into the center of the examination region. In this technique, a marking line is projected onto a patient bed bearing the patient and the patient bed is moved by an operator of the MR system such that this marking line runs through the area to be examined or the local coil, in order to reference the position of the area to be examined, or the position of the local coil. The travel path can thus be determined. Care must be taken so that the laser beam does not strike an eye of the patient, since otherwise damage to the affected eye can occur. Therefore the patient must possibly close his eyes, and the operator of the MR system has to monitor this. Such a method is described in DE 195 08 715 A1, for example.